On July 1st, Toshiba Corporation's Semiconductor Company and Storage Products Company consolidated to form Semiconductor & Storage Products Company.This page describes reliability information of semiconductor products.

General Usage Considerations

[As of April, 2011]

Design

To achieve the reliability required by an electronic device or system, it is important not only to use the semiconductor device in accordance with specified absolute maximum ratings and operating ranges, but also to consider the environment in which the equipment will be used, including factors such as the ambient temperature, transient noise and current surges, as well as mounting conditions which affect semiconductor device reliability. This section describes general design precautions. Be sure to refer to the respective technical datasheets of each product at the time of design.

Absolute Maximum Ratings


	The absolute maximum ratings of a semiconductor device are a set of ratings that must not be exceeded, even for a moment. Do not exceed any of these ratings. Exceeding the rating(s) may cause the device breakdown, damage or deterioration, and may result injury by explosion or combustion.

If the voltage or current on any pin exceeds the absolute maximum rating, the overvoltage or overcurrent causes the device’s internal circuitry to deteriorate. In extreme cases, heat generated in internal circuitry can fuse wiring or cause the semiconductor chip to break down. If the storage or operating temperature exceeds the absolute maximum rating, the device internal circuitry may deteriorate and the bonded areas may open or the package airtightness may deteriorate due to the differences between the thermal expansion coefficients of the materials from which the device is constructed.

Although absolute maximum ratings differ from product to product, they essentially concern the voltage and current at each pin, the allowable power dissipation, the connecting area temperatures, and storage temperatures. Note that the term "maximum rating" which appears in the respective technical datasheets and the like refers to "absolute maximum rating."

Operating Range

The operating range is the range of conditions necessary for the device to operate as specified in the respective technical datasheets and databooks. Care must be exercised in the design of the equipment. If a device is used under conditions that do not exceed absolute maximum ratings but exceed the operating range, the specifications related to device operation and electrical characteristics may not be met, resulting in a decrease in reliability.
If greater reliability is required, derate the device’s operating ranges for voltage, current, power and temperature before use.

Derating

The term "derating" refers to ensuring greater device reliability by setting operating ranges reduced from rated values and taking into consideration factors such as current surges and noise.
While derating generally applies to electrical stresses such as voltage, current and power, and environmental stresses such as ambient temperature and humidity. Power devices in particular have relatively large self-heating, therefore the level of junction temperature (Tj) derating greatly affects reliability.
For your reference, details are provided in the appendix. Be sure to read the appendix carefully.

Unused Pins

If unused pins are left open, some devices exhibit input instability, resulting in faulty operation such as a sudden increase in current consumption. In addition, if unused output pins on a device are connected to the power supply, GND or other output pin, the IC may malfunction or break down.
Since the treatment of unused input and output pins differs for each product and pin, please follow the directions in the respective technical datasheets and databooks.
CMOS logic IC inputs, for example, have extremely high impedance. If an input pin is left open, it can readily pick up noise and become unstable. In this case, if the input reaches an intermediate level, both the P-channel and N-channel transistors will become conductive, allowing unnecessary power supply current to flow. It is therefore necessary to ensure that the unused input gates of a device are connected to the power supply pin or ground (GND) pin of the same device. For treatment of heat sink pins, refer to the respective technical datasheets and databooks.

Latch-up

Semiconductor devices sometimes transition to an inherent condition referred to as "latch-up." This condition mainly occurs in CMOS devices. This happens when a parasitic PN-PN junction (thyristor structure) built in the device itself is turned on, causing a large current to flow between the power supply voltage and GND, eventually causing the device to break down.
Latch-up occurs when the voltage impressed on an input or output pin exceeds the rated value, causing a large current to flow in the internal element, or when the voltage impressed on the power supply voltage pin exceeds its rated value, forcing the internal element to breakdown. Once the element falls into the latch-up state, even though the excess voltage may have been applied only for an instant, the large current continues to flow between the power supply voltage and GND, potentially causing device explosion or combustion. To avoid this problem, observe the following:

Do not allow the voltage levels on the input and output pins to rise above the power supply voltage or decrease below GND. Consider the timing during power supply activation as well.
Do not allow any abnormal noises to be applied to the device.
Set the electrical potential of unused input pins to the power supply voltage or GND.
Do not create an output short.

Input/Output Protection

Wired-AND configurations in which outputs are connected together directly cannot be used since the outputs short-circuit with the configurations. Outputs should, of course, never be connected to the power supply voltage or GND. In addition, products with tri-state outputs can undergo IC deterioration if a shorted output current continues for a long period of time. Design the circuit so that the tri-state outputs will not be enabled simultaneously.

Load Capacitance

Certain devices exhibit an increase in delay times and a large charging and discharging current if a large load capacitance is connected, resulting in noise. In addition, since outputs are shorted for a long period of time, wiring can become fused. Use the load capacitance recommended for each product.

Thermal Design

The failure rate of semiconductor devices largely increases as the operating temperatures increase. As shown in Figure 1, the thermal stress applied to device internal circuitry is the sum of the ambient temperature and the temperature rise caused by the power consumption of the device. For thermal design, therefore, refer to the precautions stated in the respective technical datasheets and databooks.
To achieve even higher reliability, take into consideration the following thermal design points:

Conduct studies to ensure that the ambient temperature (Ta) is maintained as low as possible, avoiding the effects of heat generation from the surrounding area.
If the device’s dynamic power consumption is relatively large, conduct studies regarding use of forced air-cooling, circuit board composed of low thermal resistance material, and heat sinks. Such measures can lower the thermal resistance of the package.
Derate the device’s absolute maximum ratings to minimize thermal stress from power consumption.

Figure 1 Thermal Resistance of Package

θja = θjc + θca
θja = (Tj - Ta)/P
θjc = (Tj - Tc)/P
θca = (Tc - Ta)/P

where, θja:

Thermal resistance between junction and ambient air (°C/W)

θjc:

Thermal resistance between junction and package surface, or internal thermal resistance (°C/W)

θca:

Thermal resistance between package surface and ambient air, or external thermal resistance (°C/W)

Tj:

Junction temperature or chip temperature (°C)

Tc:

Package surface temperature or case temperature (°C)

Ta:

Ambient temperature (°C)

P:

Power consumption (W)

Interfacing

When connecting devices with different input and output voltage levels, make sure that the input voltage (V_IL/V_IH) and output voltage (V_OL/V_OH) levels match. Otherwise, the devices may malfunction. In addition, when connecting devices with different power supply voltages, such as in a dual power supply system, device breakdown may result if the power-on and power-off sequences are incorrect. For device interface details, refer to the respective technical datasheets and databooks. In addition, if you have any questions about interfacing, contact your nearest Toshiba office or distributor.

Decoupling

Spike currents generated during switching can cause power supply voltage and GND voltage levels to fluctuate, causing ringing in the output waveform or a delay in the response speed. (The power supply and GND wiring impedance is normally 50 to 100Ω.) For this reason, the impedance of the power supply lines with respect to high frequencies must be kept low. Specifically, this is ideally accomplished by routing thick and short power supply and GND lines and by inserting decoupling capacitors (of approximately 0.01 to 1µF) as high-frequency filters between the power supply and GND into each required location on the circuit board.
For low-frequency filtering, it is appropriate to insert a 10 to 100µF capacitor in each circuit board. However, conversely if the capacitance is excessively large (such as 1000µF), latch-up may result. An appropriate capacitance value is therefore required.
On the other hand, in the case of high-speed logic ICs, noise is caused by reflection, crosstalk or common power supply impedance. Reflections cause increased signal delay, ringing, overshoot and undershoot, thereby reducing the device’s noise margin. One effective wiring measure for preventing reflections is to reduce the wiring length by increasing the mounting density so as to lower the wiring inductance (L) and capacitance (C). This measure, however, also requires consideration with regard to crosstalk between wires. In actual pattern design, both of these factors must be considered.

External Noise

When externally induced noise or surges are applied to a printed circuit board with long I/O signals or signal lines, malfunction may result, depending on the device. To protect against noise, protective measures against surges must be taken such as lowering the impedance of the signal line or inserting a noise-canceling circuit.
For details of required protection, refer to the respective technical datasheets and databooks.

Electromagnetic Interference

Radio and TV reception problems have increased in recent years as a result of increased electromagnetic interference radiated from electrical and electronic equipment. To use radio waves effectively and to maintain the quality of radio communications, each country has defined limitations for the amount of electromagnetic interference which can be generated by designated devices.
The types of electromagnetic interference include noise propagated through power supply and telephone lines, and noise from direct electromagnetic waves radiated from equipment. Different measurement methods and corrective actions are used for each type.
Difficulties in countering electromagnetic interference derive from the fact that there is no means for calculating at the design stage the strength of the electromagnetic waves produced from each component in a piece of equipment. As a result, it is after the prototype equipment has been completed that measurements are taken using dedicated instruments to determine for the first time the strength of the electromagnetic interference. Yet it is possible during system design to incorporate measures for the prevention of electromagnetic interference which can facilitate corrective action after design completion. One effective method, for example, is to design the product with several shielding options, and then select the optimum shielding method based on the results of the measurements subsequently taken.

Peripheral Circuits

In many cases semiconductor devices are used with peripheral circuits and components. The input and output signal voltages and currents in these circuits must be designed to match the specifications of the device, taking into consideration the factors below.

Input voltages and currents that are not appropriate with respect to the input pins may cause malfunction. Some devices contain pull-up or pull-down resistors, depending on specifications. Design your system taking into account the required voltage and current.
The output pins on a device have a predetermined external circuit drive capability. If a drive capability exceeding this value is required, either insert a compensating circuit or take that fact into account when selecting components for use in external circuits

Safety Standards

Each country and region has established safety standards which must be observed. These safety standards sometimes include requirements for quality certification systems and insulation design standards. The safety standards of the respective countries and regions must be taken fully into account to ensure compliant device selection and design.

Other

When designing a system, incorporate fail-safe and other measures according to system application. In addition, debug the system under actual mounting conditions.
If a plastic package device is placed in a strong electric field, surface leakage may occur due to charge-up, resulting in malfunction. When using such a device in a strong electric field, take measures by, for example, protecting the package surface with a conductive shield.
With some memory devices and microcomputers, attention is required at power on or reset release. To ensure that your design is device appropriate, refer to the respective technical datasheets and databooks.
Design the casing so as to ensure that no conductive material (such as a metal pin) can drop from an external source onto a terminal of a mounted device, causing a short.